The Other Lamb Plot: What's the story?

For her entire life, the cult she was born into has been all that teenage Selah (Raffey Cassidy) has known. Along with a band of similarly cloistered young women she lives seemingly unstuck in time, cut off from modern society in a remote forest commune presided over by a man called Shepherd (Michiel Huisman), a controlling, messiah-like figure with a frightening dark side. But when her insular world is rocked by a series of nightmarish visions and disturbing revelations, Selah begins to question everything about her existence—including her allegiance to the increasingly dangerous Shepherd.